1. Field of the Invention
The present invention relates generally to clutch control units for vehicles and, more particularly, to a clutch control unit for automatically engaging and disengaging the clutch by learning.
2. Description of the Prior Art
FIG. 3 shows an automatic transmission using a conventional clutch control unit of this type. A well-known parallel axis gear type transmission 1 is controlled by a transmission actuator 2 which consists of a select actuator 2a and a shift actuator 2b. Each of these actuators 2a and 2b is controlled under a hydraulic pressure of a hydraulic drive unit 3 which consists of a tank 3a, a pump 3b, an accumulator 3c, and a hydraulic pressure switching electromagnetic valve (not shown) to shift a driving gear of the transmission 1 via a piston rod 2c or 2d. This control is made by the central processing unit (CPU) of a transmission drive unit 2e, which in turn is controlled by a main control unit 4 which consists of a CPU, a random access memory (RAM) and a read only memory (ROM) through serial communications.
A pair of potentiometers 2f and 2g are provided to detect the positions of the piston rods 2c and 2d, respectively, for controlling the gear position. More specifically, the actual position signals from the respective potentiometers 2f and 2g are fed back to the drive unit 2e so that they match the target position signals from the main control unit 4. An input shaft sensor 5a detects the rate of rotation v of an input shaft 1a of the transmission 1, and a vehicle speed sensor 5b detects the vehicle speed or rate of rotation V' of an output shaft of the transmission 1. The output of each of these sensors 5a and 5b is inputted to the main control unit 4.
A clutch 6 is linked to the piston rod 7a of a clutch actuator 7 for making connection or disconnection. The clutch actuator 7 is supplied with a hydraulic pressure from the hydraulic drive system 3 and subjected to a feedback control by the CPU of a clutch drive unit 7b so that the position signal of the piston rod 7a detected by the potentiometer 7c matches the target position signal from the main control unit 4. The clutch drive unit 7b is also controlled by the main control unit 4 through serial communications. An engine 8 has a control unit 8a controlled by the main control unit 4. An engine speed sensor 9 detects the rate of rotation V of an output shaft 8b of the engine 8. The rotation of the engine 8 is transmitted to an axle 10 via the clutch 6 and the transmission 1.
The output of the engine speed sensor 9 is inputted to the main control unit 4, to which more signals are inputted from an accelerator pedal sensor 11, a brake pedal sensor 12, a key switch 13, an exhaust brake switch 14, and a selector 15 to control the drive unit 2e, the clutch drive unit 7b, the engine control 8a, a display panel 16, and a control unit 17a which controls a gear position display panel 17. Thus, the main control unit 4 controls the clutch 6 and the transmission 1 according to the amount of pressdown of the accelerator pedal, the vehicle speed, and the shift position of the selector 15. The gear position is controlled by the select actuator 2a and the shift actuator 2b in response to the operation of the selector 15. If the set position is "1", "2", "3", or "R", it is controlled into the first, second, third, or reverse gear. If the set position is an automatic gear shift "4" or "5" , it is controlled based on the gear shift map according to the amount of pressdown of the accelerator pedal and the vehicle speed. The automatic gear shifts "4" and "5" provide gear shifts between the first and the fourth gear and the second and the fifth gear, respectively.
The clutch 6 is disengaged and engaged by the main control unit 4 via the clutch drive unit 7b and the clutch actuator 7 before and after the gear shift operation. This control is made according to the clutch characteristic which is obtained by a learning activity under predetermined conditions. This learning activity will be described with reference to FIG. 4. A learning starting point S has been stored in the memory of the main control unit 4. When predetermined conditions, such as the gear is set in the neutral, are met, the activity starts from the learning starting point S toward engagement of the clutch 6 to determined a half clutch point F based on the rates of rotation V and v detected by the engine speed sensor 9 and the input shaft sensor 5a. Then, the clutch starting point Q and the clutch completion point P are determined by taking predetermined offset lengths (operational distances) 1.sub.1 and 1.sub.2 toward the disengagement and engagement condition, respectively, from the half clutch point F. From the half clutch point F, the clutch starting point Q, and the clutch completion point P, a clutch characteristic M is constructed and stored in the memory. In the next learning cycle, the previous clutch starting point Q is taken as a new learning starting point S to perform a learning activity. The engagement and disengagement of the clutch 6 are controlled according to the clutch characteristic M to reduce the operational stroke of the clutch 6, thereby not only speeding up the gear shift but also providing the optimal clutch control taking the wear of the clutch 6 into consideration.
In the above conventional clutch control unit, only a single half clutch point is determined by learning, but the Japanese Patent Application Kokai No. 60-34525 has proposed that two points--a clutch completion point and a engagement starting point--are determined by learning.
As has been described above, in a vehicle equipped with the automatic transmission unit using a dry type clutch, a learning activity at the clutch meet point is necessary. However, it takes a few seconds for the whole learning activity including the determination of only a half clutch point so that if the driver moves the selector before the learning activity is completed, the learning activity is interrupted and failed.